As a wireless communication system to transmit a wide-band digital signal of video information or the like, with high quality, a wireless LAN or a wireless video transmitting system using a microwave or a millimeter wave is developed. Furthermore, from the standpoint of monitoring control in smaller factories or large-scale production facilities, anticrime monitoring for facility, disaster-prevention monitoring for a depopulated region, and the like, a sensor network configuration using a wireless system is examined.
In a normal wireless communication device, a transmitter side performs a modulating process or the like at an intermediate frequency of several ten megahertz to several hundred megahertz, depending on situations, an intermediate frequency in a several-GHz band at which signal processing is performed, and synthesizes the signal with a signal from a local oscillator to convert (up-convert) the frequency of the resultant signal into a transmission frequency in, e.g., a 60-GHz band, and emits the signal from an antenna through an electric supply line. The receiving side amplifies a wireless frequency signal from a receiving antenna, synthesizes the amplified signal with a signal from the local oscillator to convert (down-convert) the frequency of the resultant signal into an intermediate frequency band, and then performs channel extraction and signal demodulation. In the configuration, a technical difficulty occurs with an increase in frequency, and problems such as deterioration of efficiency of a local oscillator which is requested for a high-stable and sufficiently large output and deterioration of efficiency of a wireless device, for example, a loss in a frequency converter are posed. Furthermore, an increase in cost prohibits significant wireless network from being practically used and popularized.
In contrast to this, an attempt at an active antenna in which an antenna and a wireless frequency circuit section are integrated to aim at a low cost and a configuration of a radiating oscillator in which amplifier element and an electromagnetic wave radiating structure are integrated with each other are proposed. The configuration of the radiating oscillator is very simple, and is expected to be able to be applied as a constituent part of a low-cost wireless network.
As configurations of the wireless network, Bluetooth which has been practically used and a series of IEEE802.11 wireless standards known as a name of Wi-Fi are known. On the other hand, although the speed is lower than hundred times the speed of the above configuration, ZigBee which is supposed to be able to configure a low-power-consumption network at a low cost is being popularized.
The ZigBee is a technique corresponding to the standard of IEEE802.15.4 and is attractive as a short-distance, low-speed wireless link. However, like the Bluetooth or the Wi-Fi, in terms of use of frequencies, the ZigBee is a 2.4-GHz-band wireless system which is considerably busy in recent years.
On the other hand, furthermore, when wide-band digital information transmission by a 60-GHz-band millimeter wave to at a high frequency is to be performed, if phase noise and frequency stability of a local oscillator of the frequency converter are not sufficient, a wide-band digital signal cannot be transmitted with high quality due to frequency drift and phase noise. In order to solve the problem, a self-heterodyne wireless communication device technique and a wireless system configuration technique based thereon are disclosed.
For example, in self-heterodyne schemes disclosed in Japanese Patent Application Laid-Open No. 2005-348332 (to be referred to as Patent Document 1 hereinafter) and Japanese Patent Application Laid-Open No. 2003-198259 (to be referred to as Patent Document 2 hereinafter), although a local oscillator used in a transmitter is inexpensive and has an unstable frequency, a frequency shift or phase noise generated by the local oscillator are completely canceled in signal detection, and it is confirmed that a signal is preferably transmitted to a millimeter-wave-band wireless LAN or a wireless video transmission system which severely requests phase noise and frequency stability.
Furthermore, in Japanese Patent Application Laid-Open No. 2003-244016 (to be referred to Patent Document 3 hereinafter), re-conversion of a frequency required when a wireless communication network system including an application of relay to another system is constituted, i.e., conversion into a wireless transmission frequency is performed again through a conversion process to an intermediate frequency. However, at this time, in order to cope with a problem of causing deterioration in quality of a wide-band digital signal by frequency drift and phase noise when performance for phase noise or frequency stability of a local oscillator of a frequency converter is not sufficient, a technique that constitutes a system that wirelessly supplies a high-stable reference signal is disclosed.
Japanese Patent No. 3146260 (to be referred to as Patent Document 4 hereinafter), Japanese Patent No. 3355337 (to be referred to as Patent Document 5 hereinafter), and Non-patent Document 1 “R. A. Flynt, J. A. Navarro and K. Chang, ‘Low Cost and Compact Active Integrated Antenna Transceiver for System Application’, IEEE Trans. Microwave Theory Tech., Vol. 44, pp. 1642 to 1649, 1996” disclose an example of a radiating oscillator constituted by a structure of a planar resonator using a transistor as a negative resistance amplifier. Non-patent Document 1 discloses a configuration of a two-way communication apparatus in which radiating oscillators are arranged such that facing transmission/reception signals are orthogonal polarized waves and which is operated as a receiver by a mixer diode for frequency conversion.
In Non-patent Document 2 “C. M. Montiel, L. Fan and K. Chang, ‘A Self-Mixing Active Antenna for Communication and Vehicle Identification Applications’, 1996IEEE MTT-S Digest, TU4C pp. 333 to 336, 1996” discloses a technique in which a gun diode is used as an oscillation element, a high-frequency voltage is superposed on a bias voltage of the gun diode to cause frequency modulation, the modulated frequency is irradiated on a gun diode oscillator manufactured like the gun diode to cause an injection synchronization phenomenon, at the same time, the frequency modulation component is transmitted to another radiating oscillator, and, although two-way transmission and reception cannot be simultaneously performed by a mixer operation of the gun diode itself, a high-frequency signal component can be communicated.
As described above, a sensor network which avoids a large number of unsolved problems such as a problem of interference with a existing busy wireless system and problems of interference and coexistence by a high-density arrangement of wireless devices and which covers a large number of observation points in a wide region, a new wireless device technique to realize a simple wireless communication network, a wireless network configuration technique using the wireless device technique are almost developed.
However, in a conventional wireless device technique and a conventional wireless network configuration technique, a configuration is complicated to increase the cost accordingly, and poses a problem with respect power consumption or signal quality. The problem considerably obstructs practical use and popularization of a wireless network.
The present invention has been made to solve the above problems, and has as its object to provide a microwave-band-to-millimeter-wave-band wireless network system which uses a very simple configuration as a configuration of a basic wireless communication device and is suitable for a low-cost and low-power-consumption wireless network system configuration with high-quality signals.